Theoretical yield


by kathyt.25
Tags: theoretical, yield
kathyt.25
kathyt.25 is offline
#1
Jun29-09, 10:40 PM
P: 49
1. The problem statement, all variables and given/known data
Calculate the theoretical yield of aspirin (C9H8O4).
C7H6O3 + C4H6O3 --> C9H8O4 +C2H4O2
Mass C7H6O3 = 2g
Volume C4H6O3 = 4mL


2. Relevant equations



3. The attempt at a solution
I am not sure where to go with this prolem at all. I can't just assume that the density of C4H6O3 is 1g/mL because it's not water, and the problem doesn't say to assume its density to be the same as water. All I could do was find the molar mass of each substance:

C7H6O3 = 138.13g/mol
C4H6O3 = 102.1g/mol
C9H8O4 = 180.17g/mol
C2H4O2 = 60.06g/mol

I also know that I have to find the limiting reagent, to actually determine the mass of C9H8O4, but doing that requires some more information. I know that I can just Google the density of C4H603, but if its not given in the problem then its assumed that there is another way. From what I know about calcualting the limiting reagent, you need either:
(1) mass reactant / molar mass reactant --> we don't have the mass of C4H603
OR
(2) volume reactant * density reactant / molar mass reactant --> we don't have the density of C4H603 either

So with the information provided, I have no idea how to calculate the mass of C9H8O4 (aspirin)
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Wax
Wax is offline
#2
Jun30-09, 12:33 AM
P: 148
Do you have the correct answer? It's been a while since I've done this but I'm sure I can help you figure it out.
kathyt.25
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#3
Jun30-09, 12:34 AM
P: 49
Quote Quote by Wax View Post
Do you have the correct answer? It's been a while since I've done this but I'm sure I can help you figure it out.
No, we aren't given the answers for these problems.

Wax
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#4
Jun30-09, 12:35 AM
P: 148

Theoretical yield


Is the reaction balanced?
kathyt.25
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#5
Jun30-09, 12:35 AM
P: 49
Yes it is.
Wax
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#6
Jun30-09, 12:36 AM
P: 148
Is this due tomorrow?
kathyt.25
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#7
Jun30-09, 12:37 AM
P: 49
It's due on Thursday, but there are no office hours until after the work is due, for some reason. If all else fails, I will just use the density that I found on Google for the acetic anhydride
Wax
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#8
Jun30-09, 12:38 AM
P: 148
Quote Quote by kathyt.25 View Post
It's due on Thursday, but there are no office hours until after the work is due, for some reason. If all else fails, I will just use the density that I found on Google for the acetic anhydride
Cool, we still got some time then.
Wax
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#9
Jun30-09, 12:39 AM
P: 148
This is general chemistry 1 right? I have a book, let me open it up.
Wax
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#10
Jun30-09, 12:49 AM
P: 148
Okay nevermind. LOL It's been too long for me. :X
Borek
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#11
Jun30-09, 02:31 AM
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P: 22,714
In general problem - as stated - can't be solved for the reasons OP pointed out in the first post. However, you know number of moles of salicylic acid. Try:

1. Calculate stoichiometric number of moles of acetic anhydride.
2. Calculate mass of stoichiometric anhdyride.
3. Assuming 4 mL of anhdyride mass is that you calculated iin point 3 - what would be the density of the pure anhydride?
4. Have you ever seen an organic compound with that density? Does it look realistic?
5. If not - what will be the reasonable mass of the 4 mL? Higher than stoichiometric? Lower than stoichiometric?
6. So, what is in excess?

Could be that's off and that's not what you are expected to do, but for me that gives clear answer to the problem.

Anhydride density is very close to 1 g/mL.


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